The long term objective of this project is to understand more clearly the process whereby populations of functional lymphocytes are generated, focusing specifically on a subpopulation of B cells, Ly-1 B (CD5+ B cells). These cells show numerous distinctions from the "conventional" set of B cells, including an apparent predisposition to anti-self responses. Indeed, the human counterpart of this population appears involved in human diseases with autoimmune aspects, such a rheumatoid arthritis and Sjogren's syndrome. As yet, the relationship of these cells to other B cells remains unclear, although some data suggest that they may arise early in development as a completely independent B cell lineage. In this project we seek to understand when Ly-1 B cells are generated, how they relate to conventional B cells and how their bias toward self specificities occurs. We will do this in two ways: 1) defining a Ly-1 B differentiation pathway using retroviral marking of precursors specifically enriched either by sorting or by in vitro cultivation; 2) examining immunoglobulin V gene usage in Ly-B both early and late in its development by analyzing Ly-1 B hybridomas and by constructing immunoglobulin- gene enriched cDNA libraries. Specificities encoded by these V genes to be examined in detail will include both anti-thymocyte and anti-bromelain-treated mouse erythrocyte autoantibodies, both distinctively enriched in this population.